Although the submaximal graded exercise test (GXT) has become popular for the detection of preclinical ischemic heart disease, its predictive accuracy in asymptomatic subjects is low. The accuracy increases to 85 percent with serial testing, and the measurement of systolic time intervals (STI's) can greatly enhance predictive power. It is proposed to perform serial GXT's and pre- and post-exercise STI's at each annual examination of men participating in the Multiple Risk Factor Intervention Trial (MRFIT) in Newark. MRFIT, a multiple center collaborative Federally-sponsored clinical trial aimed at determining whether treatment of multiple risk factors (hypercholesterolemia, hypertension, smoking) reduces coronary mortality, is being carried out in 12,000 high risk men, age 35-57, in control and experimental groups, with a six-year follow up. A baseline submaximal GXT was performed but has not been performed again as part of the national protocol. Continuation of GXT's at the Newark Center is an ancillary study requiring outside funding. Tests are being carried out annually in the 632 men attending the Newark Clinic utilizing a Marquette Series 3500 Exercise System recording on paper and magnetic tape and an Irex Continue Trace 101 recorder, with computer analysis of the tapes at the MRFIT ECG Center, in Halifax, Nova Scotia. Data will be processed by the MRFIT Coordinating Center, where analyses will also be done. Analysis will be made of conversion rates of GXT's and changes in fitness levels. In addition to enhancing the power of the MRFIT these studies in this uniquely valuable population should demonstrate the ability to make the GXT a more accurate predictor of future coronary events and potential use of the test as an endpoint in clinical trials. These studies should indicate the utility of STI's as an adjunct to GXT and elucidate the effect of other lifestyle changes on exercise habits.